It is known to make insulators that are essentially constituted by a rod of resin or glass fibres bonded by resin, with the said rod being covered with a vulcanised sheet and/or with vulcanised fins. Two methods are commonly used to cover the rod: either the system of fins is moulded en masse on the rod, or else independent fins are threaded over the rod (which is usually sheathed) and are then glued end-to-end on the rod. The first method is advantageous for protecting the rod since it is possible to obtain a continuous covering of the rod. However, it lacks flexibility since each different size of insulator requires a different mould, and further the undercut portions of the fins present difficulties, particularly on long insulators. The second method has two drawbacks: firstly, the fins often require the presence of an adhesive or adhesion primer, generally in the form of a liquid that often contains solvents; secondly, the inter-sleeve joint between fins does not protect the rod sufficiently, in particular against ingress of moisture. This is very inconvenient for use with high-tension insulators because of the high risk of electric arcs occurring at the joint, said arcs damaging the protection of the rod and sometimes making the whole assembly unusable as an insulator.
Preferred implementation of the present invention provides a simplified version of the above mentioned second method, which avoids the use of a foreign body such as an adhesive or an adhesive primer, and obtains an insulator which is reliable over time, both electrically and mechanically.